In internal combustion engines the valves are operated by cams which are coupled to the valves through a mechanism which has deflection or compliance. Direct acting valve trains comprising only a mechanical or hydraulic lifter as the coupling mechanism are quite stiff, meaning that they have little compliance. On the other hand, some valve trains employ push rods, rocker arms, etc which introduce more compliance. In addition, there can be clearance or lash between elements of a valve train when the cam is not applying a load. In any of these systems the cam quickly applies a load to the valve train which results in noise and impact force loading of the valve train. It is desirable to avoid such results by a design which preloads the valve train prior to applying the opening force to the valve so that the compliance and clearance is removed.
The U.S. Pat. No. 4,852,527 to Beardmore et al discloses a low noise valve train which proposes a particular cam design to account for valve train deflection. The design has bluff shaped pre opening and post closing ramps which respectively provide for rapid compression and relaxation of the valve train. The design results in decreased noise and impact force on the valve train, however the cam shape is complex and may be difficult to manufacture.